Make all exception classes inherit from std::exception

This refactors out a very common pattern of formatting "%s: %s" with
e.function.c_str() and strerror( e.the_errno ) into just the what()
method of NetworkException. It's also a prerequisite for making cleaner
public API for any exceptions we throw, and allows us to more easily
get exceptions passed back to us to handle.

src/frontend/mosh-client.cc

@@ -34,7 +34,6 @@
 #include "version.h"
 
 #include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 
 #include "stmclient.h"
@@ -177,11 +176,11 @@ int main( int argc, char *argv[] )
 
     client.shutdown();
   } catch ( const Network::NetworkException& e ) {
-    fprintf( stderr, "Network exception: %s: %s\r\n",
-	     e.function.c_str(), strerror( e.the_errno ) );
+    fprintf( stderr, "Network exception: %s\r\n",
+	     e.what() );
   } catch ( const Crypto::CryptoException& e ) {
     fprintf( stderr, "Crypto exception: %s\r\n",
-	     e.text.c_str() );
+	     e.what() );
   } catch ( const std::string& s ) {
     fprintf( stderr, "Error: %s\r\n", s.c_str() );
   }

src/frontend/mosh-server.cc

@@ -311,12 +311,12 @@ int main( int argc, char *argv[] )
   try {
     return run_server( desired_ip, desired_port, command_path, command_argv, colors, verbose, with_motd );
   } catch ( const Network::NetworkException& e ) {
-    fprintf( stderr, "Network exception: %s: %s\n",
-	     e.function.c_str(), strerror( e.the_errno ) );
+    fprintf( stderr, "Network exception: %s\n",
+	     e.what() );
     return 1;
   } catch ( const Crypto::CryptoException& e ) {
     fprintf( stderr, "Crypto exception: %s\n",
-	     e.text.c_str() );
+	     e.what() );
     return 1;
   }
 }
@@ -491,11 +491,11 @@ int run_server( const char *desired_ip, const char *desired_port,
     try {
       serve( master, terminal, *network );
     } catch ( const Network::NetworkException& e ) {
-      fprintf( stderr, "Network exception: %s: %s\n",
-	       e.function.c_str(), strerror( e.the_errno ) );
+      fprintf( stderr, "Network exception: %s\n",
+	       e.what() );
     } catch ( const Crypto::CryptoException& e ) {
       fprintf( stderr, "Crypto exception: %s\n",
-	       e.text.c_str() );
+	       e.what() );
     }
 
     #ifdef HAVE_UTEMPTER
@@ -727,13 +727,13 @@ void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &network
 
       network.tick();
     } catch ( const Network::NetworkException& e ) {
-      fprintf( stderr, "%s: %s\n", e.function.c_str(), strerror( e.the_errno ) );
+      fprintf( stderr, "%s\n", e.what() );
       spin();
     } catch ( const Crypto::CryptoException& e ) {
       if ( e.fatal ) {
         throw;
       } else {
-        fprintf( stderr, "Crypto exception: %s\n", e.text.c_str() );
+        fprintf( stderr, "Crypto exception: %s\n", e.what() );
       }
     }
   }

src/frontend/stmclient.cc

@@ -568,7 +568,7 @@ void STMClient::main( void )
         throw;
       } else {
         wchar_t tmp[ 128 ];
-        swprintf( tmp, 128, L"Crypto exception: %s", e.text.c_str() );
+        swprintf( tmp, 128, L"Crypto exception: %s", e.what() );
         overlays.get_notification_engine().set_notification_string( wstring( tmp ) );
       }
     }

src/frontend/terminaloverlay.h

@@ -40,6 +40,7 @@
 
 #include <vector>
 #include <limits.h>
+#include <exception>
 
 namespace Overlay {
   using namespace Terminal;
@@ -173,10 +174,10 @@ namespace Overlay {
       show_quit_keystroke = s_show_quit_keystroke;
     }
 
-    void set_network_exception( const NetworkException &e )
+    void set_network_exception( const std::exception &e )
     {
       wchar_t tmp[ 128 ];
-      swprintf( tmp, 128, L"%s: %s", e.function.c_str(), strerror( e.the_errno ) );
+      swprintf( tmp, 128, L"%s", e.what() );
 
       message = tmp;
       message_is_network_exception = true;